The invention concerns a self-switching means for repetitively operating an electromagnetic launcher.
Electromagnetic launchers, such as rail guns and coaxial launchers are well known, and were the major subject of publication in the IEEE Transactions on Magnetics, Volume MAG-20, No. 2, March 1984, containing several individually authored articles discussed below. Kolm et al, for example, discusses in "Basic Principles of Coaxial Launch Technology" the advantages of coaxial launches, in that no physical contact with the projectile occurs, coaxial launches develop thrust over the length of the projectile, and for a given current, may yield a thrust of 100 times higher than that of a rail gun. However, the current must be synchronized with projectile motion and the voltage required increases with desired velocity. Kolm et al. point out that present research is directly almost entirely towards rail guns because they are simpler.
A basic rail gun is disclosed in "Switching for Electric Rail Guns" Barber et al. Here, a commutation switch is located at the breech of a rail gun, which is normally closed to permit the charging of an inductive energy store by a power supply. Once charging is complete, the switch is opened and current is commutated into the gun. When the projectile leaves the muzzle, the switch is closed to permit recharging of the inductor. Accordingly to Barber et al. the critical parameters are voltage recovery rate and maximum stand-off voltage. The voltage recovery rate must exceed the rate at which the railgun develops voltage.
In an effort to determine the computation of force occurring on a railgun projectile, Marshall analyzes "The Current Flow Patterns in Rail Gun Rails." Woodson discusses in "Switching Overview-Fundamental Issues" the importance of a railgun switching system. Accordingly to Woodson, time is critical regarding: how long the switchng system must carry current before switching operation occurs, how fast current is to be transferred from the switch to the load, and how fast and high the load voltage will rise.
Another time consideration is whether the switch will be single shot or repeated. Sze et al. developed a magnetically actuated switch utilizing butt contacts which permits higher current densities. Magnetic forces are used to separate the contacts. Sze et al.'s device is disclosed in their article, "Design and Testing of a Magnetically Operated Rep-rate Opening Switch." A rod array triggered vacuum gap switch is proposed by Honig in "Switching Considerations and New Transfer Circuits for Electromagnetic Launch Systems," wherein it is recognized that resistive transfer circuits require that an opening switch dissipate energy associated with load inductance and with its own inductance.
A metal, vapor vacuum arc switch was proposed by Cope et al. for a typical EM Launcher in "Metal Vapor Vacuum Arc Switching: Applications and Results." "A Coaxial Radial Opening Switch for a Distributed-Energy-Store Rail Launcher" was present by Upshall et al. in an attempt to overcome the difficulties associated with switching. Many of these articles address the realization that switchng is the critical, limiting step, in achieving rapid fire with EM Launchers. However, the authors have only proposed, at most, variations on a theme of mechanical switches, each being limited by its own operation and recycle times.
The energy efficiency of the normal rail gun, as defined by the ratio of energy in the projectile to energy lost from the energy store, is inherently low because a large amount of energy is transferred to the various inductances in the circuit and all of the energy must be dissipated (wastefully) after the projectile being accelerated (PBA) is launched. By launching multiple projectiles, as above, without requiring that the current flow cease between them, the energy stored in the stray inductances is dissipated only once rather than for each projectile. Hence there is potential for greatly increased energy efficiency.